public class xiti3_7_2{
  public static void main(String[] args) {
    int i=1,n=20;
    double sum = 0, item =1;
    for(i=1;i<=n;i++){
      sum=sum+item;
      i=i+1;
      item=item*(1.0/i);
    }
    System.out.println(sum);
  }
}
